1. Field of the Invention
The present invention relates to an image recording device and to an optical fiber, and in particular, to an image recording device which records an image onto a recording medium by main scanning and subscanning a light beam onto the recording medium by relatively moving the light beam and the recording medium, and to an optical fiber used in the image recording device.
2. Description of the Related Art
Conventional image recording devices have been known in which a laser beam outputted from a light source such as a laser is inputted to an optical fiber. The light emitted from the optical fiber is collected by a lens. While a drum, on whose outer peripheral surface a recording medium is set, is rotated in a main scanning direction, the collected light beam is scanned in the subscanning direction which is orthogonal to the main scanning direction. In this way, the image is recorded onto the recording medium which is disposed at the focal point position of the lens. For example, WO 97/27065 discloses an image recording device in which light emitted from an optical fiber array, to which infrared lasers are inputted, is focused on a drum by a telecentric lens optical system, so as to record an image. In these image recording devices, a usual optical fiber having a core/clad structure having a core of a circular cross-sectional configuration is used. The profile of the light emitted from an optical fiber having a core of a circular cross-sectional configuration is circular, and the spot configuration of the beam scanned on the recording material is also circular.
However, by carrying out exposure at a high illumination intensity and in a short time, in order to reduce the energy used for exposure, it is preferable for the spot configuration of the scanned beam to be, rather than circular, short in the main scanning direction.
Further, by making the light intensity substantially constant in the widthwise direction, variations in the widths of the written lines, which variations are caused by variations in the amount of light, can be suppressed. A stable, good image can thereby be obtained. Therefore, it is preferable that the spot configuration of the scanned beam is rectangular or the like, rather than circular.
A scanned beam spot having an elongated configuration or a rectangular configuration can be obtained by using as a light source a broad-area-type semiconductor laser (with which the profile of the emitted light is an elongated configuration or a rectangular configuration). A broad-area-type semiconductor laser is high output, and is effective for applications requiring a high output light source, such as the recording of images onto a heat-mode-type photosensitive recording material. However, because the light source is high output, much heat is generated. In cases in which light sources are disposed in an array, cooling thereof is difficult. Further, when a semiconductor laser is built-in into the optical unit of an image recording device as the output source of the scanning beam, a problem arises in that, when the semiconductor laser malfunctions, it is troublesome to replace the semiconductor laser with a new one.
Japanese Patent Application Laid-Open (JP-A) No. 7-276701 discloses an image recording device which carries out recording by laser light outputted from an optical fiber which is formed such that the output end portion thereof is shaped to have a flat surface in the vertical direction. The object of the invention of JP-A-7-276701 is to obtain pixels having no convexities nor concavities, by forming the optical fiber to have a flat surface in the vertical direction at the output end portion of the optical fiber. However, the drawings of JP-A-7-276701 only illustrate an optical fiber having an external configuration in which a circular-tube-shaped fiber is flattened midway along the fiber, and JP-A-7-276701 does not clearly disclose the material, refractive index, or structure of the optical fiber. Thus, it can only be concluded that this device utilizes a single-composition optical fiber having a uniform refractive index. With such an optical fiber, there are the problems that the light propagation loss is great and the efficiency of utilizing the light beam is markedly low. Further, an optical fiber whose shape is flattened midway along the fiber has the problem that production thereof is difficult because the produceability and reproducibility of the optical fibers is poor.
As described above, it has until now not been possible to realize an image recording device which can obtain a beam spot having an elongated configuration in the subscanning direction or a beam spot having a rectangular configuration by using an optical fiber.
The present invention was developed in consideration of the above-discussed problems with conventional image recording devices, and an object of the present invention is to provide an image recording device in which a beam spot of a configuration which extends in an elongated manner in the subscanning direction or a beam spot of a rectangular configuration can be obtained, and which can be suitably used in recording onto heat-mode-type photosensitive recording materials. Further, another object of the present invention is to provide an image recording device in which, even if the amount of light or the sensitivity of the recording material or the like varies, a stable, good image can be obtained, and which has a low propagation loss, can be manufactured easily, and is practical.
The present inventors conducted experiments in order to overcome the above-discussed problems, and as a result, overcame the above problems by the following means.
A first aspect of the present invention is an image recording device for recording an image on a recording medium by main scanning and subscanning a light beam with respect to the recording medium by relatively moving the light beam and the recording medium, comprising a light source which emits a laser beam which has been modulated in accordance with image data; an optical fiber having a core, a clad covering the core, a light exit portion, and a light entry portion optically joined to the light source, which receives the laser beam into the optical fiber, the core having a cross-sectional configuration in a plane substantially orthogonal to an optical axis direction of the laser beam corresponding to at least one of an elongated configuration and a configuration having two parallel sides at least at the light exit portion of the optical fiber; and a focusing lens which focuses, on the recording medium, a light beam emitted from the light exit portion of the optical fiber.
A second aspect of the present invention is the image recording device of the first aspect, wherein the focusing lens focuses the laser beam on the recording medium such that a configuration of the laser beam on the recording medium is the elongated configuration and the elongated configuration includes a short dimension oriented in a direction coinciding with a direction in which the main scanning is conducted.
A third aspect of the present invention is the image recording device any one of the first aspect and the second aspect, wherein the cross-section of the core is the elongated configuration and the elongated configuration includes a short dimension oriented in a direction coinciding with a direction in which the main scanning is conducted.
A fourth aspect of the present invention is the image recording device of the first aspect, wherein the cross-section of the core is configuration having two parallel sides, and the focusing lens focuses the laser beam on the recording medium such that a light intensity of the light beam emitted from the light exit portion of the optical fiber is substantially same at least one of in a direction in which the main scanning is conducted and in a direction in which the sub scanning is conducted.
A fifth aspect of the present invention is the image recording device any one of the first to forth aspects, wherein the recording medium is a heat-mode-type photosensitive recording material.
A sixth aspect of the present invention is the image recording device any one of the first to fifth aspects, wherein the light source is a broad-area-type semiconductor laser.
A seventh aspect of the present invention is an optical fiber for transmitting a light beam, comprising: a core having a light entry portion for receiving a light beam therein a light exit portion and a cross-sectional configuration in a plane substantially orthogonal to an optical axis direction of the light beam being at least one of an elongated configuration and a configuration having two parallel sides at least at the light exit portion; and a clad covering the core.
An eighth aspect of the present invention is the optical fiber of the seventh aspect, wherein an exit light beam emitted from the light exit portion of the optical fiber having a light intensity distribution in one of directions substantially orthogonal to the optical axis direction is a single-mode distribution.
A ninth aspect of the present invention is the image recording device any one of the first to sixth aspects, wherein an exit light beam emitted from the light exit portion of the optical fiber having a light intensity distribution in a direction in which the main scanning is conducted is a single-mode distribution.
A tenth aspect of the present invention is the image recording device any one of the first to sixth and ninth aspects, wherein the optical fiber is formed from at least two optical fibers, and the at least two optical fibers are disconnectably joined by a joining member which is provided with positioning means at peripheries of the optical fibers for positioning the optical fibers relative to one another according to a predefined orientation.
A eleventh aspect of the present invention is an image recording device which records an image on a recording medium by main scanning and subscanning a light beam with respect to the recording medium by relatively moving the light beam and the recording medium, and in which a plurality of light beams are main scanned in a single main scan, comprising: a plurality of light sources emitting light beams which have been modulated in accordance with image data; an optical fiber array in which a plurality of optical fibers are aligned in an array form such that positions of the optical fibers in a focal point direction are the same, each of the optical fibers including a light entry portion, a light exit portion, and a core, the core having a cross-sectional configuration in a plane substantially orthogonal to an optical axis direction of each of the light beams corresponding to at least one of an elongated configuration and a configuration having two parallel sides at least at the light exit portion of the optical fiber, and each the optical fiber including a clad covering each the core, the plurality of optical fibers being optically joined to the light source; and a focusing lens which focuses, on the recording medium, light beams emitted from the light exit portions of the optical fibers.
A twelfth aspect of the present invention is the image recording device of the eleventh aspect, wherein the focusing lens focuses the laser beam on the recording medium such that a configuration of the laser beam on the recording medium is the elongated configuration and the elongated configuration includes a short dimension oriented in a direction coinciding with a direction in which the main scanning is conducted.
A thirteenth aspect of the present invention is the image recording device any one of the eleventh and twelfth aspects, wherein the cross-section of the core is the elongated configuration and the elongated configuration includes a short dimension oriented in a direction coinciding with a direction in which the main scanning is conducted.
A fourteenth aspect of the present invention is the image recording device of the eleventh aspect, wherein the cross-section of the core is configuration having two parallel sides, and the focusing lens focuses the laser beam on the recording medium such that a light intensity of the light beam emitted from the light exit portion of the optical fiber is substantially same at least one of in a direction in which the main scanning is conducted and in a direction in which the sub scanning is conducted.
A fifteenth aspect of the present invention is the image recording device any one of the eleventh to fourteenth aspects, wherein the plurality of optical fibers are aligned such that no intervals are formed between focused images on the recording material. In accordance with the first aspect of the invention, due to the cross-sectional configuration the core of the light exit portion of the optical fiber being at least one of an elongated configuration and a configuration having two parallel sides, the beam spot formed on the recording medium can also be formed in at least one of an elongated configuration and a configuration having two parallel sides. In the second aspect, a configuration of the laser beam on the recording medium is the elongated configuration and the elongated configuration includes a short dimension oriented in a direction coinciding with a direction in which the main scanning is conducted. As a result, the scanning time is short. Further, a reduction in energy is achieved when a recording material exhibiting low intensity reciprocity law failure is used. Further, by using the optical fiber having the core/clad structure as the light transfer route, the amount of light required for image recording can be obtained with a low propagation loss.
In accordance with the third aspect of the invention, the cross-section of the core is the elongated configuration and the elongated configuration includes a short dimension oriented in a direction coinciding with a direction in which the main scanning is conducted. Thus, a beam spot, whose short dimension direction coincides with the main scanning direction, can be obtained on the recording medium with a simpler lens system.
In accordance with the forth aspect of the invention, the cross-section of the core is configuration having two parallel sides. Thus, the intensity of the light of beam is substantially constant in the widthwise direction. Therefore, even if the light amount or the sensitivity of the recording material or the like varies, there is little variation in the widths of the written lines and in the halftone dot ratio. A good, stable image can therefore be obtained.
Much attention has been paid to heat-mode-type photosensitive recording materials as digital plate-making systems, from the standpoint of writing images directly onto a recording material by a laser. In accordance with the invention of the fifth aspect, by using a low amount of exposure energy, a good image can be obtained on a heat-mode-type photosensitive recording material which exhibits low intensity reciprocity law failure.
In the sixth aspect of the present invention, a high output light beam can be obtained by using a broad-area-type semiconductor laser. Further, because the profile of the emitted light of a broad-area-type semiconductor laser is an elongated configuration or configuration having two parallel sides, the efficiency of light entering into an optical fiber having an elongated core cross-section or configuration having two parallel sides, which is same as the profile of the emitted light of the broad-area-type semiconductor laser, is good.
In accordance with the ninth aspect of the present invention, the spot diameter in the main scanning direction is easy to control by using an optical fiber which emits a light beam having a single-mode main scanning direction light intensity distribution.
In accordance with the tenth aspect of the invention, it is easy to disconnect the light sources and the recording head. Thus, if a light source malfunctions and can no longer be used, the light source can be easily replaced. Further, at the joining means, a positioning means is provided around the optical fiber. Thus, the light exiting end surfaces of the cores of the respective optical fibers can be made to coincide when the optical fibers are joined. Thus, the loss of light due to coupling of the optical fibers can be kept low.
In accordance with the eleventh aspect of the invention, a plurality of light beams can be main scanned in a single main scan, such that the speed of image formation can be increased. Further, the light sources are optically joined to the recording head or the like by the optical fibers whose lengths can be adjusted. Thus, the light sources and the recording head can be disposed apart from one another, which facilitates cooling of the light sources.
In accordance with the fifteenth aspect of the present invention, the configurations of the pixels formed on the recording medium by the scanned beam can be adjusted, such that a better image can be obtained.